1. FIELD OF THE INVENTION
The present invention relates to a hydraulic control system for controlling a flow control valve to drive a hydraulic actuator in response to operation of a manual control device (such as a control lever or control pedal).
2. DESCRIPTION OF THE RELATED ART
The hydraulic control system noted above includes a position sensor for detecting shift positions of the manual control device. The flow control valve is operable to a position corresponding to a shift position of the manual control device detected by the sensor.
According to this control system, when the manual control device lies in a neutral stop position, the control valve is also placed in a neutral position to maintain the hydraulic actuator in a standstill state. As the manual control device is shifted from the neutral stop position to an operative position, the control valve is opened by an amount corresponding to the position of the control device, such that pressure oil is delivered at the higher flow rate from the control valve, the greater the amount of operation of the control device.
Thus, the hydraulic actuator is operable at the higher rate, the greater amount the control lever is operated from the neutral stop position. By selecting a shift position of the manual control device, the hydraulic actuator may be driven at a desired speed. That is, the shift position of the manual control device and the opening amount of the control valve are in a one-to-one relationship.
Thus, when it is desired to slightly move a working implement standing still, the manual control device must be shifted from the neutral stop position slightly to an operative position. This opens the control valve slightly, which in turn operates the hydraulic actuator slightly.
In practice, however, it is difficult for the operator to shift the manual control device from the neutral stop position to an operative position by a precise, slight amount. The manual control device is, more often than not, shifted from the neutral stop position to excess. Thus, slightly moving the working implement standing still requires a difficult operation.